One area of use for high-quality UV interference filters is in lithography in the production of semiconductor components, inter alia. By way of example, interference filters are used in so-called steppers in order to filter out as far as possible monochromatic light from the spectrum of the vapor lamps that are usually used. In a stepper, a wafer, or the applied photoresist, is exposed stepwise via a mask projected onto the wafer in demagnified fashion.
In many cases the i-line of the mercury of a mercury vapor lamp is used for this purpose. Particular requirements arise here in respect of the filter for filtering out this light. At shorter wavelengths, the tolerances in the optical thickness of the interference layers also decrease correspondingly. The tolerances have to be complied with not just in the case of a newly incorporated filter; stringent requirements are made of long-term stability, too. Here neither the transmission nor the position of the edges of the transmission window or windows should change over a relatively long time.